Silicone polyethers are generally prepared by reacting an alkenyl functional polyether such as an allyl polyether with a polyorganohydrogensiloxane in the presence of a platinum catalyst. In the preparation of these silicone polyethers, an excess of, for example, allyl polyether is used, and, in doing so under the conditions of the addition reaction, a portion of the allyl polyether is rearranged into propenyl polyether which is orders of magnitude slower at undergoing the addition reaction. The reaction product thus contains the silicone polyether copolymer as well as moieties of unreacted allyl polyether and unreacted propenyl polyether. These silicone polyethers are often used as active ingredients in cosmetic products. However, in some formulations they contribute a strongly noticeable, distinct and unpleasant, acrid odor which has a tendency to become stronger upon storage. The odor is generally understood to arise as a consequence of the oxidation and/or hydrolysis of the unreacted propenyl ether into propionaldehyde. This odor is an obstacle to the use of these silicone polyethers as active ingredients in many cosmetic preparations.
Attempts have been made in the past to prevent the formation of or remove the odor forming components and have involved a combination of the addition of a heterogeneous hydrogenation catalyst, hydrogenation (i.e. exposure to hydrogen gas), and some form of an acid-catalyzed hydrolysis followed by vacuum stripping. For example Japanese Patent Application No. 07330907 discloses the manufacture of a purified polyether-modified polysiloxane composition synthesized by the hydrosilylation reaction of a polyoxyalkylene with a C.dbd.C in the terminal position and a polyhydrogensiloxane. The polyether-modified polysiloxane composition is then hydrogenated in the presence of an added heterogeneous hydrogenation catalyst to saturate any residual double bonds. This has the effect of preventing the unwanted degradation of the propenyl ether; thereby preventing the formation of the odorous propionaldehyde. Other volatile components are preferably distilled off from the reaction mixture before or after hydrogenation.
Japanese Patent Application No. 9165315 discloses a skin cosmetic material which contains 0.01 to 100 wt % of a purified polyether-modified polysiloxane composition prepared by the hydrosilylation reaction of a polyoxyalkylene with a carbon-carbon double bond in the terminal position and a polyhydrogensiloxane. The material is then purified by hydrogenation in the presence of an added heterogeneous hydrogenation catalyst.
Japanese Patent Application No. 9165318 discloses a hair cosmetic containing 0.01 to 100 wt % of a purified polyether-modified polysiloxane composition prepared by the hydrosilylation reaction of a polyoxyalkylene containing a C--C double bond at the terminus with a polyhydrogensiloxane, followed by hydrogenation in the presence of an added heterogeneous hydrogenation catalyst.
Heinrich et al. in U.S. Pat. No. 5,225,509 discloses a method for deodorizing polyoxyalkylene polysiloxane mixed block copolymers wherein the polysiloxane blocks are linked to the polyether blocks through SiC linkages. Heinrich et al further discloses that hydrogen is allowed to act on the mixed block polymers in the presence of heterogeneous hydrogenation catalysts at temperatures of 20 to 200.degree. C. and a pressure of 1 to 100 bar for a period of 0.5 to 10 hours. Heinrich et al. only discloses the use of heterogeneous hydrogenation metal catalysts or supported metals. Nowhere in Heinrich et al. are homogeneous transition metal hydrosilylation catalysts and in particular homogeneous platinum hydrosilylation catalysts disclosed or suggested as hydrogenation catalysts.